Originally Posted by LarDasse74

This should not be happening at all. Your wheels were not properly tensioned and/or stress relieved when they were built. Did you build them yourself? If so - live and learn - get a tensiometer and retension them properly.
Did you have a professional build them? If so, shame on him/her. Take the wheels back and and ask how much tension the spokes were brought to during the build... I'll guess they say "as tight as we put every wheel we build - tight enough but not too tight!" (this is not an acceptable response, imho)

Becauser you are a bigger guy, your spokes need to be a little tighter than the average joe. I do not know what sort of tightness this equates to in kgf, but others here do. Listen to them, and you should probably learn to build your own wheels, or call around and see if anyone else in your town has a more experienced wheel builder.

FWIW, I am 270 lbs and my 32 spoke wheels hold up fine for my 14km loaded commute on a dirt road - because I laced them myself and put the spokes goddamn tight!